The following formula (I) can be attributed to the methyl esters of arylpropionic acids obtainable according to the present invention: ##STR1## wherein R stands for an aryl group, preferably a phenyl, diphenyl or a naphthyl group, also substituted with groups inert under the reaction conditions.
Processes for the preparation of arylpropionic acids esters are known in general. Thus, for instance, it is known to carbonylate styrene in the presence of ethyl alcohol and of palladium diphosphine complexes.
In this way there are obtained mixtures of ethyl 2- and 3-phenylpropionate in varying rates and, in some cases, also with remarkable selectivities, while the same cannot be said with regard to the enantioselectivity towards an optical isomer. Moreover, the parametric operational conditions of the reaction, 120.degree. C. for 16 hours under a pressure of 200 Kg/sq.cm. of carbon monoxide, evidently appear less suited for an industrial application because of their drasticity.
Other processes foresee the carbonylation of the olefins in the presence of palladium complexes with ligands of the phosphoric, nitrylic, olefinic type and with atoms of halides (chlorine).
Nonetheless, also in this case, the results described as to the selectivity do not correspond to the results when tested from the enantioselectivity point of view, which constitutes the original aspect of the process conducted according to this invention.
Summing up, it may be generally maintained from the examination of the previously cited literature that, even if under more drastic conditions of temperature and carbon oxide pressure, it is possible to adjust in the desired direction the selectivity or, better still, the regioselectivity of the reaction within a rather wide range, making recourse to different types of catalysts and especially to different phosphines as the ligands for the palladium catalyst.
However, from the same literature it may be learned that the results of a good regioselectivity are not accompanied by equally good results from the point of view of the enantioselectivity, or at least there are not remarkable as possible equally good results.